Catalyst for treating wastewater, process for producing it, and process for treating wastewater with the catalyst

ABSTRACT

The present invention provides a catalyst used in wastewater treatment process wherein not only an organic compound not containing nitrogen, sulfur or halogen is decomposed, but also a nitrogen-containing compound, a sulfur-containing compound and an organic halogeno compound are effectively decomposed, thereby wastewater are treated with excellent efficiency for a long period of time. The invention also provides a production process for the catalyst and said wastewater treatment process. The first catalyst comprises: an oxide of iron as an A component; and at least one kind of element as a B component selected from a group consisting of cobalt, nickel, cerium, silver, gold, platinum, palladium, rhodium, ruthenium and iridium. The second catalyst comprises: an oxide as an A component containing iron and at least one kind of element selected from a group consisting of titanium, silicon and zirconium; and at least one kind of element as a B component selected from a group consisting of cobalt, nickel, cerium, silver, gold, platinum, palladium, rhodium, ruthenium and iridium.

This application is a continuation-in-part of application Ser. No.07/878,978, filed May 6, 1992, now pending.

BACKGROUND OF THE INVENTION

The present invention relates to a catalyst which is used for wetoxidation treatment for wastewater containing organic compounds etc. andused for decomposing them and also relates to a process for producingthe catalyst and a process for treating wastewater with the wetoxidation under the presence of the catalyst.

There have been hitherto known methods for treating wastewater, such asa biochemical method called the activated-sludge method, a wet oxidationtreatment called the Zimmerman method.

The activated-sludge method requires a long time to decompose organiccompounds and also requires to dilute wastewater up to a concentrationsuitable for the growth of algae and bacteria so that it has a defectthat a large scale of area is required to set treating facilities.

The Zimmerman method comprises treating wastewater in the presence of anoxygen gas under a high temperature and high pressure and decomposingorganic compounds in the wastewater. In this method, there has beenproposed a method which comprises a use of various kinds of oxidationcatalysts in order to accelerate a reaction rate. The oxidation catalystused here is a catalyst with a compound of a noble metal such aspalladium, platinum or the like supported on a carrier such as alumina,silica, silica gel, active carbon or the like.

In general, it is rare that the chemical species included in wastewaterto be treated is always the same. Thus, there are many cases where anitrogen-containing compound is included besides a nitrogen-free organiccompound.

However, wastewater including a nitrogen-containing compound such as anamine compound, an amide compound, an amino acid compound or the like isnot treated with satisfactory efficiency by the above-mentioned methods.

Wastewater including an amine is usually treated by a cohesive treatingmethod in which an anionic macromolecule cohesive agent is used. Thismethod comprises gathering an amine by the anionic macromoleculecohesive agent and eliminating a formed precipitate (or sludge) fromwastewater. Also, there has been attempted an adsorbent method whichcomprises bringing wastewater in contact with various kinds ofadsorbents such as active carbon, activated clay, a silica gel, acomplex oxide gel and the like, and adsorbing the amine to the adsorbentfor eliminating it from the wastewater

Since sludge formed by the cohesive treating method contains amines, itshould not be abolished without a following treatment. Because of this,a treatment to decompose the amines in the sludge becomes necessary. Inaddition, the macromolecular cohesive agent is expensive, so a cost forthe treatment becomes high.

Concerning the adsorbent method, the elimination percentage of amines isnot satisfactory enough. Since the adsorbing power of an adsorbenteasily decreases, there is a problem in durability of the adsorbent.

Since the wet oxidation process is unavoidable in the wastewatertreatment, it will be convenient if an arrangement is made so as todecompose a nitrogen-containing compound included in the wastewater inthe course of the wet oxidation process.

On the other hand, a treatment for wastewater including asulfur-containing compound has been so far carried out by a respectivelydifferent method depending upon the state and nature of thesulfur-containing compound. For example, in a case of wastewaterincluding an organic sulfur compound, a biological treatment isgenerally carried out. However, in a case where a compound containingthiophene and the like is treated, which affects badly upon organisms insludge, a biological treatment can not be applied and, accordingly, acombustion treatment etc. are carried out.

Wastewater containing a sulfide such as sodium sulfide or the like: forexample, wood digestion wastewater in paper- and pulp manufacture,wastewater coming out from a coke oven in steel manufacture, wastewaterafter fiber-washing, wastewater from a plant of petroleum chemicalproducts such as ethylene, BTX and the like, as well as wastewater froma coal gasification plant, a petroleum-refining plant, a rayon factoryand a dyeing plant; has been mostly treated by a method which comprisesadding iron chloride into wastewater to solidify sulfur ions, removingsolid iron sulfide by solid-liquid separation, adjusting pH of theseparated solution, carrying out a biological treatment of the solution,and then discharging the treated wastewater. Also, wastewater containinga sulfite salt and thiosulfate salt: for example, wastewater coming outfrom a wood kiln of pulp-making factory, wastewater fromphotograph-developing, wastewater from metal treatment as well asalkaline wastewater used to absorb sulfur dioxide and the like; istreated by a method which comprises subjecting wastewater toneutralization-precipitation treatment followed by biological treatmentand then discharging the treated wastewater.

When wastewater containing a sulfur-containing compound is treated byeither one or both of biological treatment and combustion treatment,there exist the undermentioned problems to be solved. In the biologicaltreatment, it is necessary to adjust a wastewater source solution bydiluting it with water so that organisms are not badly affected.Therefore, wastewater to be treated becomes a large amount andfacilities for the biological treatment must be arranged in a largescale, so that there is a serious problem is in the necessary cost andso forth.

Also, in the combustion treatment, when a heal amount generating fromwastewater is low, a supplementary fuel must be added and also, becausea large amount of sulfur is usually included in the wastewater, a largeamount of sulfur oxides are formed and, therefore, it is necessary toarrange a desulfurizer.

Next, when wastewater including a sulfur-containing compound such assulfide is treated, if a method which comprises removing thesulfur-containing compound as iron sulfide by adding iron chloride isapplied, sludge having iron sulfide as a main component is formed andalso, this method is complicate as a treating procedure, because itconsists of the following steps: injection of solution of chemicals,solid and liquid separation, pH control and biological treatment

The organic halogeno compounds have been used for various kinds of usagebecause of their stability. Since they are nonflammable and has greatcapability to degrease, they have been used in a large amount as adegreasing cleaner in metal, machinery and electronics industries aswell as a cleaner for dry cleaning. On the other hand, the compoundshave brought about problems on various fields. In general, since theorganic halogeno compounds are difficult in decomposition, they areseriously accumulating in the natural environment and, as a result,ground water pollution has emerged everywhere. Furthermore, some of theorganic halogeno compounds have been found to have carcinogenic natureagainst human bodies and, thus, trichloroethylene, tetrachloroethylene,1,1,1-trichloroethane and the like have been designated as regulationitems of the water-pollution preventive law on 1989, because of concernabout influence on the human health.

Concerning treatment of the organic halogeno compounds, various methodshave been proposed or used, and if the methods are roughly classified,there are a degradation method and a nondegradation method. Concerningthe degradation method, there are listed a packed tower strippingmethod, a volatilizing method by means of exposing to air or heating,and an adsorption method using active carbon or macromolecules.Concerning the volatilizing method, the operation itself is very simpleand at a low cost, but the method comprises only evaporating organichalogeno compounds in a liquid phase or a solution and scattering themin air and, therefore, basically it does not settle environmentalpollution caused by organic halogeno compounds. Concerning theadsorption method, a secondary processing such as a recovering processafter adsorption and a process to treat an adsorbent becomes necessary.

Concerning the degradation method, there are listed an irradiationmethod, a microorganism degradation method, a redox method and so forth.The irradiation method, of which representative examples are aphotodecomposition method using a semiconductor as a catalyst and aradiation-irradiating method using a radiation, is still on anexperimental stage and can not be adopted for a practical use. Themicroorganism degradation method takes a long time for treatment and itsefficiency in treatment is unstable and, therefore, there exist manyproblems for a practical use. Concerning the redox method, a method ofusing an oxidizing agent such as ozone, hydrogen peroxide or the likeand a method of reductive degradation method using iron have beenattempted.

However, in a case where an organic halogeno compound exists in a highconcentration, a method of highly efficient treatment has not yet beeninvented either as a nondegradation method or as a degradation method.In the volatilizing method, a large amount of organic halogeno compoundsare discharged into air and, therefore, the method is not fundamentalsolution for the organic halogeno compounds to be-treated. Theadsorption method is short in the break-through time in a case of highconcentration, so it is not practical. Concerning the degradationmethod, highly effective decomposition has not yet been a practical one,and also, there exists a problem that harmful decomposition products aresecondarily generated. In short, a practical and fundamental method toremove the organic halogeno compounds is not yet developed at a presentstage.

SUMMARY OF THE INVENTION

Accordingly, it is the first object of the present invention to providea catalyst for treating wastewater which not only decomposes an organiccompound not containing nitrogen, sulfur or halogen, but also decomposeseffectively a nitrogen-containing compound, a sulfur-containing compoundand an organic halogeno compound, whereby the wastewater treatment canbe carried out with good efficiency for a long period of time. Thesecond object of the present invention is to provide a process forproducing an above type catalyst for treating wastewater with goodefficiency. In addition, the third object of the present invention is toprovide a process for treating wastewater with good efficiency for along period of time, whether the wastewater includes anitrogen-containing compound, a sulfur-containing compound or an organichalogeno compound or not.

To solve the first object, the present invention first provides acatalyst for treating wastewater, comprising: an oxide of iron as an Acomponent; and at least one kind of element as a B component, which isselected from a group consisting of cobalt, nickel, cerium, silver,gold, platinum, palladium, rhodium, ruthenium and iridium. The presentinvention second provides a catalyst for treating wastewater,comprising: an oxide as an A component, which contains iron and at leastone kind of element selected from a group consisting of titanium,silicon and zirconium; and at least one kind of element as a Bcomponent, which is selected from a group consisting of cobalt, nickel,cerium, silver, gold, platinum, palladium, rhodium, ruthenium andiridium.

To solve the second object, the present invention first provides aprocess for producing a catalyst for treating wastewater, comprising thefollowing steps: obtaining a coprecipitate containing iron and at leastone kind of element selected from a group consisting of cobalt, nickel,cerium, silver, gold, platinum, palladium, rhodium, ruthenium andiridium; and calcinating the coprecipitate. The present invention secondprovides a process for producing a catalyst for treating wastewater,comprising the following steps: obtaining an oxide of iron; and makingthis oxide contain at least one kind of element selected from a groupconsisting of cobalt, nickel, cerium, silver, gold, platinum, palladium,rhodium, ruthenium and iridium. The present invention third provides aprocess for producing a catalyst for treating wastewater, comprising thefollowing steps: obtaining a coprecipitate containing iron and at leastone kind of element selected from a group consisting of titanium,silicon and zirconium; calcinating the coprecipitate, in order to obtainan oxide containing iron and at least one kind of element selected froma group consisting of titanium, silicon and zirconium; and making thisoxide contain at least one kind of element selected from a groupconsisting of cobalt, nickel, cerium, silver, gold, platinum, palladium,rhodium, ruthenium and iridium.

To solve the third object, the present invention first provides aprocess for treating wastewater, comprising wet oxidation treatment ofthe wastewater by using a solid catalyst under a condition that anoxygen gas is supplied at a pressure maintaining the wastewater in aliquid phase; being characterized in that a catalyst used as said solidcatalyst contains the following two components: an oxide of iron as an Acomponent; and at least one kind of element as a B component, which isselected from a group consisting of cobalt, nickel, cerium, silver,gold, platinum, palladium, rhodium, ruthenium and iridium. The presentinvention second provides a process for treating wastewater, comprisingwet oxidation treatment of the wastewater by using a solid catalystunder a condition that an oxygen gas is supplied at a pressuremaintaining the wastewater in a liquid phase; being characterized inthat a catalyst used as said solid catalyst contains the following twocomponents: an oxide as an A component, which includes iron and at leastone kind of element selected from a group consisting of titanium,silicon and zirconium; and at least one kind of element as a Bcomponent, which is selected from a group consisting of cobalt, nickel,cerium, silver, gold, platinum, palladium, rhodium, ruthenium andiridium.

Wastewater to be treated in this invention includes a nitrogen-freeorganic compound, a nitrogen-containing compound, a sulfur-containingcompound, an organic halogeno compound or the like. The nitrogen-freeorganic compounds are, for example, aldehydes; alcohols; lower organicacids such as acetic acid, formic acid and the like. Thenitrogen-containing compounds are, for example, amine compounds, amidecompounds, amino acid compounds and the like.

The amine compound, as far as it is a compound having an amino group inthe molecule, may be any one of a primary amine, a secondary amine, atertiary amine, and a quarternary amine salt. Practical examples arealkyl amines such as methylamine, dimethylamine, trimethylamine,propylamine and the like; alkylene diamines such as ethylenediamine,trimethylenediamine and the like; alkanol amines such as ethanolamine,triethanolamine and the like, all of which are aliphatic amines. Inaddition, the examples are aromatic amines such as aniline and the like;and nitrogen-containing heterocyclic compounds such as pyridine,picoline and the like.

The amide compound is a compound containing a group (RCONH--) made bycombining an amino group with an acid group in its molecule. Practicalexamples are formamide, methylformamide, acetoamide, ethylformamide,methylpropionamide, dimethylformamide, diethylformamide,dimethylacetoamide, N-methylpyrroline and the like.

The amino acid compound is a compound containing a carboxyl group and anamino group in the same molecule and, it is called as an α-amino acid,β-amino acid, γ-amino acid or the like. Practical examples are aliphaticamino acids such as glycine, alanine, valine, leucine, serine, cystine,aspattic acid, glutamic acid, lysine, alginine and the like; amino acidshaving an aromatic ring such as phenylalanine, tyrosine and the like;amino acids having a heterocyclic ring such as histidine, tryptophan,proline and the like; and others.

However, the nitrogen-containing compound, with which this inventiondeals, is not limited to the above-mentioned examples. Thenitrogen-containing compound needs not to be under a condition ofdissolving in water and, even if it is under a condition of floating andsuspending and so forth, it can be decomposed by a treating process ofthis invention.

A nitrogen-containing compound in wastewater may exist in form of eithera sole compound or a mixture of plural kinds. The nitrogen-containingcompound in wastewater for which the present invention can be applied isnot especially limited, but its concentration is usually in a range offrom 10 to 100,000 mg/l.

The sulfur-containing compound in the present invention is an inorganicor organic compound containing at least one sulfur atom other thansulfuric acid (SO₄ ²⁻). The compound includes, for example, a sulfidesuch as hydrogen sulfide, sodium sulfide, potassium sulfide, sodiumhydrogen sulfide, sodium polysulfide and the like; thiosulfuric acidsand their salts such as sodium thiosulfate, potassium thiosulfate andthe like; sulfurous acids and their salts such as sodium sulfite and thelike; trithionic acid, tetrathionic acid, and their salts such as sodiumtrithionate; thiols such as ethylmercaptan, thiophenol,3,4-mercaptotoluene, dimercaptol, cystein and the like; thioacetals suchas diethylthioacetal , 1-ethoxy-1-(methylthio)cyclopentane cyclopentaneand the like; thiosulfites such as methyl thiosulfite, ethyl thiosulfiteand the like; sulfides such as ethylsulfide, 1-(methylthio)propane,methionine and the like; thiins such as 4H-thiin and the like;thiocarbonates and their derivatives such as trithiocarbonate, sodiumS-methyldithiocarbonate, diethyl trithiocarbonate, potassiumO-ethyldithiocarbonate, S-methyl hydrogen thiocarbonate and the like;thio-acids and their derivatives such as sodium thiosulfate,hexanethio-acid, 1-piperidinecarbodithio-acid, hexanedithio-acid,O-thioacetic acid, S-thioacetic acid, dithiobenzoic acid, sodiumdithioacetic acid, a S-ethyl ester of hexanethio-acid, an O-ethyl esterof hexanethio-acid, hexanethioyl chloride, 2-thiophenecarbothioamide,dibenzoic acid thioanhydride, di(thiobenzoic acid) anhydride and thelike; thiocyans, thiocyanic acids and their salts such as rhodan,thiocyanic acid, potassium thiocyanic acid, ammonium thiocyanic acid andthe like; thiocyanic acid esters such as methyl thiocyanate, ethylthiocyanate, allyl thiocyanate and the like; thiosaccharides such as1-thioglucose, S-methyl-5-thio-D-ribose and the like; thiazyl compoundssuch as fluorinated trithiazyl and the like; thiazines such as1,2-thiazine, 1,3-thiazine, methylene blue and the like; thiazoles suchas 1,3,4-thiadiazole, 1,3-thiazole, thioflavin, primuline and the like;thiocarbamides such as thiocarbamide, thiosemicarbamide, dithizone andthe like; thiopyranes such as α-thiopyran, γ-thiopyran,3-methyl-4H-thiopyran and the like; thiophenes such as thiophene,methylthiophene, thionaphthene, thiophthene and the like; polysulfidessuch as diphenyltrisulfide, diphenyldisulfide,1,4-bis(methyldithio)cyclohexane and the like; thioaldehyde and thelike; thioketones such as cyclohexanethione, 1,3-dithiorane-2-thione,2,4-pentanedithione and the like; sulfinyl compounds such as thionylchloride, diethylsulfoxide and the like; sulfonium compounds such astrimethylsulfonium iodide and the like; sulfonyl compounds such assulfuryl chloride, sulfonylamide, diethylsulfone, thiophene-1,1-dioxideand the like; sulfonic acids and their salts such asdodecylbenzenesulfonic acid, sodium p-toluenesulfonate,naphthalinesulfonic acid, sulfanilic acid, sulfobenzoic acid, methylorange, benzenedithiosulfinic acid and the like; sulfinic acidderivatives such as ethyl methanesulfonate and the like; sulfinic acidsand their derivatives such as 1-piperidinesulfinic acid and the like;sulfates such as dimethylsulfate, methyl hydrogen sulfate and the like;sulfamides and their derivatives such as phenylsulfamide and the like.These compounds may be soluble in an aqueous medium or exist as asuspending substance in an aqueous medium. Also, even if sulfuric acidis contained in wastewater, there is no problem for treating it.

The organic halogeno compound in this invention is an organic compoundcontaining at least one or more of a halogen atom in its molecule.Preferable examples for this are an aliphatic organic chloro compoundsuch as methyl chloride, ethyl chloride, dichlorethylene,trichloroethylene, tetrachloroethylene, 1,1,1-trichloroethane, vinylchloride and the like; an aliphatic organic bromo compound such asmethyl bromide, ethyl bromide, vinyl bromide and the like; an aromaticorganic chloro compound such as monochlorobenzene, dichlorobenzene,benzyl chloride and the like; an aromatic organic bromo compound such asbenzyl bromide, benzylidene bromide and the like; flon such astrichlorofluoromethane, dichlorofluoromethane and the like, but theexample is not limited to the above-described compounds.

Hereinafter, the first catalyst for treating wastewater, which relatesto the present invention, is explained in detail.

A feature of the first catalyst for treating wastewater of thisinvention is that, as an A component, an oxide of iron is used and, as aB component, at least one kind of element selected from a groupconsisting of cobalt, nickel, cerium, silver, gold, platinum, palladium,rhodium, ruthenium and iridium is used. A preferable form of thiscatalyst is such as a coprecipitate being calcinated, which is obtainedfrom a solution containing elements of the catalyst A and B components,rather than a simple mixture of a powder oxide of the catalyst Acomponent with a metal or compound of the catalyst B component. Thiscalcinated product of the coprecipitate is not such as an oxide of thecatalyst A component and a metal or compound of the catalyst B componentbeing simply blended, but the product is a compound formed by that thecatalyst A component and catalyst B component are well blended at amicroscopic level and, accordingly, it is considered that novelproperties not recognized in a metal or compound alone in each of the Aand B components has emerged. Meanwhile, from a viewpoint thatcapability of decomposing the nitrogen-containing compounds,sulfur-containing compounds and organic halogeno compounds are superior,a preferable B component is a metal or compound containing at least onekind of element selected from a group consisting of platinum, palladium,rhodium, ruthenium and iridium.

Preferable proportions of each catalyst component in the first catalystof this invention are, for the catalyst A component, in a range of from0.05 to 99.95% by weight as an oxide, further preferably from 50 to99.95% by weight as an oxide and, for the catalyst B component, in arange of from 0.05 to 99.95% by weight as a metal or compound, furtherpreferably from 0.05 to 50% by weight. If the catalyst's A component orB component is out of the above range, catalytic activity may beinsufficient. Or heat resistance and acid resistance may be inferior,which is unfavorable from a viewpoint of catalyst durability.

Although in this invention it is preferred to make the catalyst A and Bcomponents using a coprecipitation method, the A and B components may beprepared as complex oxides by another production process. A method tomake the catalyst A and B components using the coprecipitation method ishereinafter explained by taking the Fe₂ O₃ --CoO compound as an example(as described above, an oxide which the Fe₂ O₃ --CoO makes in a closelyblended form).

A precipitate is made by dissolving iron nitrate and cobalt nitrate inwater followed by mixing them sufficiently, and then, adding aqueousammonia to form a precipitate, which is taken by filtration, washed,dried, and calcinated at a temperature in a range of from 300° to 900°C. This method is practically carried out, for example, as follows. Theiron and cobalt source compounds (iron nitrate and cobalt nitrate) aretaken in order to have a defined value in a weight ratio of Fe₂ O₃ andCoO and, under a condition of an acidic aqueous solution, to have theconcentration in a range of from 1 to 100 g per liter upon convertinginto the oxides or iron and cobalt (Fe₂ O₃ and CoO), and a solutionobtained as described above is maintained at a temperature in a range offrom 10° to 100° C. With stirring, into this solution is added dropwisean aqueous ammonia as a neutralizing agent and, then, an obtainedmixture is allowed to react for a time in a range of from 2 to 10,whereby a coprecipitated compound (a precipitate) comprising iron andcobalt is formed. A thus-formed coprecipitate is taken by filtration,well washed, dried at a temperature in a range of from 80° C. to 140° C.for a period of time in a range from 1 to 10 hours, and calcinated at atemperature in a range of from 300° to 900° C. for a period of time in arange from 1 to 10 hours, whereby a Fe₂ O₃ --CoO compound is obtained.

In this invention, to obtain a catalyst by the coprecipitation method,it is necessary to dissolve elements of the catalyst A and B componentsin water. To dissolve an element of the catalyst A component, that isiron, into water, a water-soluble iron compound may be dissolved intowater. To dissolve an element of the catalyst B component into water,for example, a water-soluble compound or sol of the element may bedissolved into water.

A preferable water-soluble iron compound (an iron source) can beselected from, for example, inorganic iron compounds such as ironnitrate, iron sulfate, iron chloride and the like as well as organiciron compounds such as iron oxalate, iron citrate and the like.

A preferable starting material of the catalyst B component is an oxide,a hydroxide, an inorganic acid salt, an organic acid salt or the likeand, for example, it is selected from an ammonium salt, oxalate, anitrate, halogenide and the like.

Slight amounts of impurities and admixtures may be contained among thesematerials. However, as far as the impurities and admixture do notsignificantly affect properties of an obtained compound, such materialsdo not cause trouble.

There are dissolved in water an iron source and a water-soluble salt ofat least one kind of element selected from a group consisting of cobalt,nickel, cerium, silver, gold, platinum, palladium, rhodium, rutheniumand iridium, and to this aqueous solution is added a basic compound suchas aqueous ammonia, urea, sodium hydroxide, potassium hydroxide and thelike to adjust the pH, whereby a precipitate is formed. The formedprecipitate is a coprecipitate containing elements of the catalyst A andB components, which is usually a hydroxide. This precipitate is driedand then calcinated to convert it into an oxide. If required, theobtained oxide may be crushed and molded. This calcination is carriedout, for example, in a temperature range of from 300° to 900° C. for aperiod of time in a range of from 1 to 10 hours, preferably, from 2 to 6hours under an air stream.

Using a compound containing the catalyst A and B components (forexample, a Fe₂ O₃ --CoO compound) prepared according to theforementioned process, a completed catalyst is obtained, for example, bythe following procedure. One example of the procedure involves that amolding additive is added to a powder of the Fe₂ O₃ --CoO compound andan obtained mixture is well mixed with adding a proper amount of water,then kneaded, and molded by a molding device into a proper type such asa pellet, sphere, honeycomb type, etc.

The moldings is dried at a temperature in a range of from 50° to 120° C.and calcinated at a temperature in a range of from 300° to 1000° C.,preferably from 350° to 900° C. for a period of time in a range from 1to 10 hours, preferably form 2 to 6 hours, whereby a catalyst isobtained.

On the other hand, it is possible that to an oxide obtained fromcalcinating an iron-containing compound is added an aqueous solution ofa metal salt of the forementioned B component together with a moldingadditive and, an obtained mixture is kneaded, molded, then dried andcalcinated. The calcinating condition is, for example, similar to a caseof calcinating the forementioned moldings.

Hereinafter, the second catalyst for treating wastewater, which relatesto the present invention, is explained in detail.

The feature of the second catalyst for treating wastewater of thisinvention is using an oxide as an A component in the catalyst, whichincludes iron (hereinafter, referred to as "component (i)") and at leastone kind of element (hereinafter, referred to as "component (ii)")selected from a group consisting of titanium, silicon and zirconium. Thecatalyst A component is, for example, a mixture of an oxide powder ofthe component (i) with an oxide powder of the component (ii). In apreferable case, a precipitate obtained from a solution containing anelement in either one member of the components (i) and (ii) is wellmixed with a salt slightly soluble in water containing an element in theother member of the components (i) and (ii) (which may be a precipitateobtained from a water-soluble salt containing an element in the othermember or may be an oxide containing an element in the other member),and the obtained mixture is calcinated to convert into an oxide, whichis then used as the catalyst A component. The calcinated product of themixture is an oxide, which is derived from a form of the components (i)and (ii) mixed at a microscopic level more intimately than the eachother's mixture of the forementioned oxide powders. A further preferablecatalyst A component is an oxide obtained by calcinating a coprecipitatewhich is lead from a solution containing the components (i) and (ii).

This calcinated compound of the coprecipitate is not a simple mixtureconsisting of an oxide of the component (i) and an oxide of thecomponent (ii), but it is a compound in which the components (i) and(ii) are well mixed at a microscopic level to form an oxide. It can berecognized that novel physical properties emerge, which are not observedin an oxide of each consisting component alone.

In the second catalyst of this invention, a preferable proportion ofeach component is 90 to 99.95% by weight for the catalyst A componentand 0.05 to 10% by weight in form of a metal or a compound for the Bcomponent. If the B component is out of the above range, the oxidationactivity may be insufficient. In addition, if the A component is out ofthe above range, the hot water resistance and acid resistance may beinsufficient, so it is unfavorable in a viewpoint of catalysisdurability. Furthermore, it is preferred that, in the catalyst Acomponent, the component (i) is in a range of from 4.95 to 95% by weightas an oxide and the component (H) is in a range of from 4.95 to 95% byweight as an oxide (here, a total of the components (i) and (ii) is in arange of from 90 to 99.95% by weight). If they deviate from theseranges, the hot water resistance and acid resistance may be insufficientand it is unfavorable in a point of catalyst durability.

In this invention, although it is preferable that the catalyst Acomponent is prepared using coprecipitation method, the A component maybe made as a complex oxide or the like by other production processes. Amethod of preparing the A catalyst component by a coprecipitation methodis hereinafter explained by taking, as an example, a case where the Acomponent is a TiO₂ --Fe₂ O₃ compound this TiO₂ --Fe₂ O₃ compound is, asdescribed above, an oxide that TiO₂ and Fe₂ O₃ make in a closely blendedform and, hereinafter, the same).

A precipitate is made by dissolving titanium sulfate (a titanium sourcecompound) and iron nitrate (an iron source compound) in water and mixingthem sufficiently, and by adding an aqueous ammonia. This precipitate istaken by filtration, washed, dried, and calcinated at a temperature in arange of from 300° to 750°. To present a concrete example, this methodis carried out as follows. That is, the above-described titanium sourcecompound and iron source compound are taken so that a weight ratio ofTiO₂ and Fe₂ O₃ is in a specific value, and under a condition of anaqueous acidic solution, the titanium and iron are adjusted to aconcentration of from 1 to 100 g per liter upon converting into oxides,and the aqueous acidic solution is maintained at a temperature in arange of from 10° to 100° C. Into this solution is added dropwise withstirring an aqueous ammonia as a neutralizing agent and, an obtainedsolution is stirred for a period of from further 10 minutes to 3 hoursat a pH in a range of from 2 to 10, whereby a coprecipitated compound (acoprecipitate) consisting of titanium and iron is formed. The formedprecipitate is taken by filtration, well washed, dried at a temperaturein a range of of from 80° to 140° C. for a period of from 1 to 10 hours,and calcinated at a temperature in a range of from 300° to 750° C. for aperiod of from 1 to 10 hours, whereby a TiO₂ --Fe₂ O₃ compound isobtained.

In this invention, in order to obtain the catalyst A component by acoprecipitation method, it is necessary to dissolve elements of thecomponents (i) and (ii) in water. To dissolve an element of thecomponent (i) in water, for example, a water-soluble iron compound maybe dissolved in water. To dissolve an element of the component (H) inwater, for example, a water-soluble compound or sol of the element maybe dissolved in water.

A preferable water-soluble iron compound (an iron source) is selectedfrom, for example, inorganic iron compounds such as iron nitrate, ironsulfate, iron chloride and the like; and organic iron compounds such asiron oxalate, iron citrate and the like.

A preferable water-soluble titanium compound or sol (a titanium source)is selected from, for example, inorganic titanium compounds such astitanium chlorides, titanium sulfate and the like; and organic titaniumcompounds such as titanium oxalate, tetraisopropyl titanate and thelike.

A preferable water-soluble silicon compound or sol (a silicon source) isselected from, for example, inorganic silicon compounds such as colloidtype silica, water glass, silicon tetrachloride and the like; andorganic silicon compounds such as tetraethyl silicate and the like.

A preferable water-soluble zirconium compound or sol (a zirconiumsource) is selected from, for example, inorganic zirconium compoundssuch as zirconium oxychloride, zirconium nitrate, zirconium sulfate andthe like; and organic zirconium compounds such as zirconium oxalate andthe like.

In a group of these raw materials, although there exist such a member ascontaining slight amounts of impurities and mingling compounds, theimpurities and mingled compounds in a raw material cause no problem asfar as they do not affect on physical properties of an obtainingcompound.

In the group of raw materials, at least one kind of source among thetitanium, silicon and zirconium sources is dissolved with an iron sourcein water and, a precipitate is formed by varying pH with adding a basesuch as ammonia, urea, sodium hydroxide, potassium hydroxide or thelike. The precipitate formed is a coprecipitate containing elements ofthe components (i) and (ii) and is usually a hydroxide. This precipitateis dried and calcinated to convert it into an oxide. If necessary, theoxide obtained may be crushed and molded. It is preferred that thecalcinating is carried out at a temperature in a range of from 300° to750° C. for a period of from 1 to 10 hours (more preferably for 2 to 6hours) with an air stream.

Using the A component (for example, a TiO₂ --Fe₂ O₃ compound) preparedby the forementioned process, a completed catalyst is obtained, forexample, from the following process. A molding additive is added to aTiO₂ --Fe₂ O₃ compound powder and, an obtained mixture is further mixedwith adding a proper amount of water, kneaded, and molded by a moldingdevice to a proper shape such as a pellet, sphere, honeycomb type or thelike.

A molded product is dried at a temperature in a range of from 50° to120° C., and calcinated at a temperature in a range of from 300° to 750°C., preferably at a temperature in a range of from 350° to 700° C., fora period of from 1 to 10 hours, preferably for a period of from 2 to 6hours with an air stream, whereby a carrier is obtained.

An obtained carrier is soaked in an aqueous solution of a respectivemetal salt of the catalyst B component to carry the metal salt, thendried and calcinated, whereby a catalyst for treating wastewater of thisinvention is obtained. Or an aqueous solution of a metal salt of theforementioned B component together with a molding additive may be addedto the A component (for example, a TiO₂ --Fe₂ O₃ compound powder), and amixture obtained above may be kneaded, molded, then dried andcalcinated. The calcination condition is, for example, similar to a caseof calcinating the forementioned moldings.

Or again, a metal salt of the B component may be added before or aftercoprecipitation of the A component.

A preferable starting material of the catalyst B component is an oxide,a hydroxide, an inorganic acid salt, an organic acid salt or the like ofat least one kind of element selected from a group consisting of cobalt,nickel, cerium, silver, gold, platinum, palladium, rhodium, rutheniumand iridium. For example, it is selected from an ammonium salt, anoxalate, a nitrate, a sulfate, a halogenide or the like of said element.

An element of the B component is carried in a condition of a metal, acompound or the like.

Concerning the shape of a catalyst of the present invention, althoughany one of a pellet, sphere, honeycomb, ring type and the like can beused , because blocking in a catalyst layer by a solid, a precipitate orthe like may occur in a case of treating wastewater containing asuspension, the honeycomb type is especially preferred.

A preferable catalyst used in this invention is such as having aspecific composition as mentioned above. A preferable shape of thecatalyst is one-body structure such as a pellet, particle and honeycombtype or other several types of structure. A catalyst of the particletype has an average diameter in a range of from 1 to 10 mm, preferablyfrom 2 to 7 mm. If the average diameter is less than 1 mm, pressure lossincreases. If it is larger than 10 mm, the geometric surface area is notenough and sufficient treating capability can not be obtained, so thatthis is unfavorable. Relative surface area by the BET method is in arange of from 5 to 200 m² per gram, preferably, 10 to 80 m² per gram.

If it is less than 5 m² per gram, contact efficiency between moleculesto be treated and a catalyst lowers and, if it is larger than 200 m² pergram, the mechanical strength of a solid catalyst becomes weak, so thatthis is unfavorable. A catalyst of the pellet type has an averagediameter in a range of from 1 to 10 mm, preferably from 3 to 8 mm and alength in a range of from 2 to 15 mm, preferably from 3 to 10 mm. If theaverage diameter is less than 1 mm or the length is shorter than 2 mm,pressure loss may increase and, if the average diameter is larger than10 mm or the length is longer than 15 mm, the geometric surface area isnot enough, the contact efficiency diminishes, and sufficient treatingcapability may not be obtained, so that this is unfavorable. It ispreferred that relative surface area by the BET method of the pellettype catalyst is in a range similar to that in a case of the particletype. A preferable shape of a honeycomb type catalyst has a penetratinghole-corresponding diameter in a range of from 2 to 20 mm, a cell wallthickness in a range of from 0.1 to 3 mm, and an opening ratio in arange of from 50 to 90%. A further preferable shape has a penetratinghole-corresponding diameter in a range of from 2.5 to 15 a cell wallthickness in a range of from 0.5 to 3 mm and an opening ratio in a rangeof from 50 to 90%. If the penetrating hole-corresponding diameter isless than 2 mm, pressure loss is large and, if it exceeds 20 mm,although the pressure loss becomes small, the contact percentagediminishes and the catalyst activity lowers. In a case where the cellwall thickness is less than 0.1 mm, although there is an advantage thatthe pressure loss is small and a catalyst can be converted into a lightweight one, the mechanical strength of the catalyst may diminish. In acase where the cell wall thickness exceeds 3 mm, the mechanical strengthis enough, but the pressure loss may become large. From the same reasonto the above-described, a preferable opening ratio is in a range of from50 to 90%.

To carry out a process for treating wastewater of this invention, forexample, there is used a single cylindrical tube reactor for wetoxidation reaction or the like which is commonly used in ahitherto-known process for treating wastewater. A multiple tube reactorfor wet oxidation reaction or the like is used depending upon wastewaterto be treated.

In these reactors, for example, a catalyst for treating wastewater ofthis invention is arranged in a manner similar to a previous manner, andthen wastewater is subjected to a wet oxidation process.

Next, one example of treatment condition for wastewater is explained.

First, in a case of wastewater including a nitrogen-containing compound,the temperature in the course of wastewater treatment is required to beset at a temperature lower than a critical temperature in order tomaintain a liquid phase condition off, the wastewater. A temperaturelower than the critical one is properly selected, the atmospherepressure is set at a pressure higher than a pressure under which thewastewater keeps its liquid phase at said temperature. A pressure ofthis sort is, for example, in a range of from 1 to 200 kgf/cm².According to this invention, the temperature necessary for treatingwastewater can be set, for example, in a range of from 100° to 370° C.,but it is possible to set it at a temperature which is about 50° C.lower compared with a case of previous wet oxidation treatment, and inthis temperature range, decomposition of an organic compound or the likeinto carbon dioxide, water or the like as well as decomposition ofnitrogen in a nitrogen-containing compound into a nitrogen gas areachieved.

Although existence of an oxygen gas is necessary for the reaction ofwastewater treatment, air is preferable owing to its cheap cost, excepta special case where apparatus-compacting or the like is wanted. Apreferable amount of the oxygen gas is from 1 to 1.5 times of thetheoretically required oxygen amount.

The pH of wastewater necessary for wet oxidation treatment may be setcase by case between an acidic region and an alkaline region, and it is,for example, from 1 to 14.

Next, in a case of wastewater including a sulfur-containing compound,the wet oxidation process is carried out in the presence of theabove-described catalyst at a temperature of 350° C. or lower under apressure that the wastewater has a liquid phase, preferably, at atemperature lower than 180° C. under a pressure less than 10 kg/cm² Gand also, in the presence of an oxygen gas in an amount of 1 to 5 timesof a theoretical oxygen amount which is required for oxidativedecomposition of an inorganic compound containing a sulfur atom into aninorganic salt, a carbon dioxide gas, water, a nitrogen gas or the like.Besides, in a case where an organic compound contained in the wastewateris simultaneouly converted into a harmless compound, a theoreticaloxygen amount required for oxidative decomposition of the organiccompound should be added. It is considered that the sulfur atomconstituting an inorganic sulfur compound becomes harmless by beingoxidized to a sulfate ion with the wet oxidation.

In the present invention, it is preferable to adjust the pH in a rangeof from a neutral to an alkaline region, after treatment of wastewaterincluding a sulfur-containing compound is finished, by supplying analkaline component before or during the treatment. This is because theoxidation reaction by a solid catalyst of the sulfur-containing compoundis especially accelerated in a range of from a neutral to an alkalineregion. Also, that is because in a wet oxidation process under an acidiccondition that sulfuric acid exists, the material of the wet oxidationreaction tube corrodes very much, so that it is afraid that theapparatus durability is damaged very much.

Finally, in a case of wastewater including an organic halogeno compound,the wet oxidation reaction in this invention is carried out in thepresence of a specific catalyst, by keeping the wastewater at atemperature in a range of from 100° to 370° C., under a pressure whichmaintains the wastewater in a liquid phase, and in the presence of anoxygen gas in an amount equal to or more than the theoretically requiredamount to oxidize the organic halogeno compounds being contained inwastewater into carbon dioxide, water, water-soluble salts, ashes andothers. In a case where oxygen-consuming substances (hereinafter,referred to as "TOD components") such as other organic compounds etc.exists, that is a pollution factor of the wastewater, a theoreticalamount of oxygen required for oxidative degradation of the TOD componentshould be added.

In a case where the organic halogeno compounds are treated by thepresent invention, the halogen atom in the wastewater becomes harmlessby being converted into a halide ion. That is, the chlorine atom in anorganic chloro compound, the fluorine atom in an organic fluorocompound, and the bromine atom in an organic bromo compound areconverted into the Cl - ion, F - ion, and Br - ion, respectively, sothat said halogen atoms become harmless.

In this invention, it is preferred to make salts by adding beforehandinto wastewater an equivalent amount or more of cations which make pairswith halide ions generating from the wet oxidation. In adding cations,it is further preferred that alkali metal ions such as sodium, potassiumor other ions are added. By adding the alkali metal ions intowastewater, durability decrease of a reaction tube caused by thatwastewater becomes acidic in the course of treatment is prevented, andin addition, the reaction rate is accelerated, so that faster treatmentbecomes possible. As far as the alkali metal ions show an alkalinecharacter by dissolving them into wastewater, any kind of the ions canbe used and, for example, there are listed for use sodium hydroxide,potassium hydroxide, sodium carbonate, sodium acetate and the like. In acase where a salt containing an organic acid moiety such as sodiumacetate or the like is added into wastewater, the acetate ion isdecomposed up to carbon dioxide and water, similarly to the case oforganic halogeno compounds.

Concerning the oxygen-containing gas in this invention, a gas having anyoxygen concentration may be used. As the oxygen concentration in anoxygen-containing gas becomes higher, the reaction rate is moreaccelerated and faster treatment becomes possible. However, sincesufficient efficiency on treatment is obtainable even by the air, theoxygen concentration of an oxygen-containing gas may be properlydetermined depending upon factors such as cost and the like.

The first catalyst for treating wastewater of this invention contains,as an A component, an oxide of iron and, as a B component, at least onekind of element selected from a group consisting of cobalt, nickel,cerium, silver, gold, platinum, palladium, rhodium, ruthenium andiridium. This catalyst maintains its catalytic activity for a longperiod of time even if wastewater includes a nitrogen-containingcompound, a sulfur-containing compound or an organic halogeno compoundwhen the wastewater being treated with wet oxidation.

In the second catalyst for treating wastewater relating to thisinvention, the B component is at least one kind of element selected froma group consisting of cobalt, nickel, cerium, silver, gold, platinum,palladium, rhodium, ruthenium and iridium. The A component is an oxidecontaining iron and at least one kind of element selected from a groupconsisting of titanium, silicon and zirconium. This catalyst maintainsits catalytic activity for a long period of time even if wastewaterincludes a nitrogen-containing compound, a sulfur-containing compound oran organic halogeno compound when the wastewater being treated with wetoxidation.

Wastewater can be treated with excellent efficiency for a long period oftime, even if the wastewater includes a nitrogen-containing compound, asulfur-containing compound or an organic halogeno compound, bysubjecting the wastewater to wet oxidation treatment using such acatalyst as stated above, similar to a case where the wastewater doesnot include said compounds. In addition, since nitrogen in thenitrogen-containing compound is decomposed up to a nitrogen gas,post-treatment as carried out in previously known conventional methodsbecomes unnecessary.

A catalyst for treating wastewater of this invention not only decomposesa nitrogen-free organic compound, but also decomposes nitrogen in anitrogen-containing compound up to a nitrogen gas. By using thiscatalyst, whether wastewater includes a nitrogen-containing compound ornot, the wastewater treatment can be carried out for a long period oftime with excellent efficiency.

According to a catalyst for treating wastewater of this invention, acompound containing sulfur and other pollution substances in wastewatercan be decomposed by oxidation with excellent efficiency and, it ispossible to convert them into inorganic salts, carbon dioxide, water,ash or the like. Then, biological treatment is not required as apost-treatment at all and treated wastewater may be directly discharged,or even if the biological treatment is required as a post-treatment, asubstance which may affect badly on an organism has already beendecomposed and it is unnecessary to regulate wastewater on which the wetoxidation process has been carried out, except for a pH adjustment.Therefore, an amount of the treated wastewater becomes small andbiological treatment facilities are not necessary at all or they can bevery small compared with previous facilities, and treatment process issimplified. Consequently, an advantage comes on the investment andrunning cost of facilities.

According to this invention, it is possible to convert an organichalogeno compound, which is included in wastewater, into carbon dioxide,water, soluble salts, ash or the like with excellent efficiency andwhereby to make the compound harmless without secondary forming ofharmful substances.

According to a process for producing a catalyst for treating wastewaterof this invention, a superior catalyst for treating wastewater asdescribed above can be produced with excellent efficiency.

According to a process for treating wastewater of this invention,whether the wastewater includes a nitrogen-containing compound, asulfur-containing compound or an organic halogeno compound or not, it ispossible to treat wastewater for a long period of time with excellentefficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, catalyst preparation examples and wastewater treatmentexamples relating to practical examples of the present invention andcomparative catalyst preparation examples and comparative wastewatertreatment examples are shown, but the present invention is not limitedto the below-described examples.

Preparation example 1

A compound consisting of iron and ruthenium was prepared by theundermentioned process.

Into 50 liter of water were dissolved 4.81 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O] and an obtained solution was well mixed with adding500 cc of an aqueous ruthenium nitrate solution (100 g/l as Ru). To thismixture maintained at about 30° C. with well stirring, an aqueousammonia was gradually added dropwise until pH 8 being indicated, and anobtained mixture was still stood for 15 hours to make a precipitate(gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of Fe₂ O₃ and Ru, in which the weight ratio between Fe₂O₃ and Ru was 95 versus 5 according to a fluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletsof paticle diameter 5 mm φ and length 6 mm, dried at 120° C. for 6 hoursand then, calcinated at 500° C. for 3 hours.

Preparation example 2

Into 50 liter of water were dissolved 3.54 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O], 1.09 kg of cobalt nitrate and 200 cc of an aqueousplatinum nitrate solution (100 g/l as Pt), and an obtained solution waswell mixed. To this mixture maintained at about 30° C. with wellstirring, an aqueous ammonia was gradually added dropwise until pH 8being indicated, and an obtained mixture was still stood for 15 hours tomake a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcined at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of Fe₂ O₃, CoO and Pt, in which the weight ratio amongFe₂ O₃, CoO and Pt was 70:28:2 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletsof paticle diameter 5 mm and length 6 mm, dried at 120° C. for 6 hoursand then, calcinated at 500° C. for 3 hours.

Preparation example 3

Into 50 liter of water were dissolved 2.53 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O], 1.21 kg of cerous nitrate Ce(NO₃)₃ ·6H₂ O] and 200 ccof an aqueous palladium nitrate solution (100 g/l as Pd), and anobtained solution was well-mixed. To this mixture maintained at about30° C. with well stirring, an aqueous ammonia was gradually addeddropwise until pH 8 being indicated, and an obtained mixture was stillstood for 15 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of Fe₂ O₃, CeO₂ and Pd, in which the weight ratio amongCeO₂ and Pd was 50:48:2 according to a fluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletsof paticle diameter 5 mm φ and length 6 mm, dried at 120° C. for 6 hoursand then, calcinated at 500° C. for 3 hours.

Treatment examples 1 to 3

Using each of the catalysts obtained from the preparation examples 1 to3, wastewater treatment was carried out by wet oxidation according tothe following procedure.

Each of the catalysts (1000 cc) was filled in a reaction tube made of astainless steel of a wet oxidation column and, from a down part of tilereaction tube, preheated wastewater blended with air containing oxygenin a concentration of about 21% was continuously introduced for 5,000hours, the COD (Cr) concentration and total nitrogen amount weremeasured at an entrance and exit of the reaction tube to calculate theirelimination percentages. Meanwhile, wastewater to be treated contained15,000 mg/l of dimethylformamide and showed 20,000 mg/l in the COD (Cr)concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 230N liter per hour at the rate of supplyingair. Obtained results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 99.0       99.5                                         example 1 example 1                                                           treatment preparation 99.5       99.1                                         example 2 example 2                                                           treatment preparation 99.5       99.0                                         example 3 example 3                                                           ______________________________________                                    

As seen in Table 1, in a continuous operation for 5,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Treatment examples 4 to 6

According to the treatment example 1, wastewater treatment was carriedout by wet oxidation using each of the catalysts obtained from thepreparation examples 1 to 3. Wastewater to be treated contained 20,000mg/l of glycine and showed 19,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 160N liter per hour at the rate of supplyingair. Obtained results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 98.5       99.0                                         example 4 example 1                                                           treatment preparation 99.0       99.0                                         example 5 example 2                                                           treatment preparation 98.9       98.7                                         example 6 example 3                                                           ______________________________________                                    

As seen in Table 2, In a continuous operation for 3,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Treatment examples 7 to 9

According to the treatment example 1, wastewater treatment was carriedout by wet oxidation using each of the catalysts obtained from thepreparation examples 1 to 3.

Wastewater to be treated contained 10,000 mg/l of ethanolamine andshowed 12,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 140N liter per hour at the rate of supplyingair. Obtained results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 98.8       99.0                                         example 7 example 1                                                           treatment preparation 98.5       98.5                                         example 8 example 2                                                           treatment preparation 98.5       98.5                                         example 9 example 3                                                           ______________________________________                                    

As seen in Table 3, in a continuous operation for 3,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Preparation example 4

Into 50 liter of water were dissolved 10 kg of ferric nitrate [Fe(NO₃)₃·9H₂ O]. To an obtained solution maintained at about 30° C. with wellstirring, an aqueous ammonia was gradually added dropwise until pH 8being indicated, and an obtained mixture was still stood for 16 hours tomake a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 16 hours. Then, it was calcinated at 700° C. for 6 hours under anair atmosphere. According to a X-ray diffraction analysis, an obtainedpowder consisted of Fe₂ O₃.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletshaving a particle diameter 5 mmφ and length 6 mm, and calcinated at 500°C. for 4 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous ruthenium nitratesolution, dried at 120° C. for 6 hours, and calcinated at 400° C. for 4hours.

An obtained, completed catalyst showed composition having a 99.3 versus0.7 ratio by weight between Fe₂ O₃ and ruthenium, according to afluorescence X-ray analysis.

Treatment example 10

Using the catalyst obtained from preparation example 4, wastewaterhaving the below-mentioned composition was continuously treated for 1000hours under the reaction conditions of 130° C. at a reactiontemperature, 9 kg/cm² G at a reaction pressure, 1 liter per hour at therate of supplying wastewater, and 667N liter per hour at the rate ofsupplying air [ratio of O₂ /TOD (amount of oxygen in air theoreticaloxygen demand) is 2].

    ______________________________________                                        pH                  13                                                        Na.sub.2 S          8%                                                        NaSH                3%                                                        Na.sub.2 CO.sub.3   3%                                                        TOD                 100,000 mg/l                                              ______________________________________                                    

Such a treatment resulted in that COD (Cr) was 3500 mg/l or less,sulfide ion was 0.1 mg/l or less, and thiosulfate ion was 5000 mg/l orless.

Comparative preparation example 1

Into 100 liter of water were gradually dissolved 7 kg of titaniumtetrachloride(TiCl₄). To an obtained solution maintained at about 30° C.with well stirring, an aqueous ammonia was gradually added dropwiseuntil pH 8 being indicated, and an obtained mixture was still stood for16 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 16 hours. Then, it was calcinated at 600° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, an obtainedpowder consisted of TiO₂.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to aspherical shape of an average particle diameter 6 mm, and calcinated at500° C. for 4 hours under an air atmosphere.

A thus-obtained, spherically molded product was soaked in an aqueousiridium chloride solution, dried at 140° C. for 3 hours, and calcinatedat 450° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.8 versus0.2 ratio by weight between TiO₂ and Ir, according to a fluorescenceX-ray analysis.

Comparative treatment example 1

The catalyst of comparative preparation example 1 obtained by theabove-mentioned process was filled in a reaction tube. Treatment ofwastewater similar to the wastewater used in treatment example 10 wascarried out according to treatment example 10 under the conditionssimilar to treatment example 10. As a result, COD (Cr) was 11,000 mg/lor less, sulfide ion was 50 mg/l or less, and thiosulfate ion was 14,000mg/l or less.

Preparation example 5

The pellet-like molded product of the oxide of iron obtained frompreparation example 4 was soaked in an aqueous chloroplatinic acidsolution, dried at 150° C. for 4 hours, and calcinated at 450° C. for 3hours.

An obtained, completed catalyst showed composition having a 99.7 versus0.3 ratio by weight between the oxide of iron and platinum, according toa fluorescence X-ray analysis.

Treatment example 11

The catalyst, 500 cc, obtained from preparation example 5 was filled ina reaction tube. Treatment of wastewater having the below-mentionedcomposition was carried out according to treatment example 10 under theconditions of 200° C. at a reaction temperature, 50 kg/cm² G at areaction pressure, 1 liter per hour at the rate of supplying wastewater,and 220N liter per hour at the rate of supplying air [ratio of O₂ /TOD(amount of oxygen in air/theoretical oxygen demand) is 1.2]. Inaddition, other conditions were as follows.

    ______________________________________                                        Thiophene:        0.1%                                                        Sodium rhodanide: 3.0%                                                        Dimethyl sulfoxide:                                                                             1.5%                                                        TOD:              55 g/l                                                      ______________________________________                                    

The above-mentioned treatment resulted in that treated wastewatercontaining 40 mg/l or less of thiophene, 10 mg/l or less of sodiumrhodanide and 20 mg/l or less of dimethyl sulfoxide was stably obtained.In addition, TOC treatment efficiency was 83%.

Comparative preparation example 2

γ-alumina (spherical; average particle diameter 5 mm) was soaked in anaqueous palladium nitrate solution, dried at 120° C. for 5 hours, andcalcinated at 400° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.5 versus0.5 ratio by weight between the alumina and palladium, according to afluorescence X-ray analysis.

Comparative treatment example 2

The catalyst, 500 cc, obtained from comparative preparation example 2was filled in a reaction tube. Treatment of wastewater similar to thewastewater used in treatment example 11 was carried out, according totreatment example 11, under the conditions similar to treatment example11.

The above-mentioned treatment resulted in that treated wastewatercontaining 100 mg/l or less of thiophene, 1200 mg/l or less of sodiumrhodanide and 900 mg/l or less of dimethyl sulfoxide was stablyobtained. In addition, TOC treatment efficiency was 61%.

Preparation examples 6 to 11

The pellet type molded product of the oxide of iron obtained frompreparation example 4 was soaked in an aqueous solution of one kindamong ruthenium nitrate, chloroauric acid, palladium nitrate, iridiumchloride, silver nitrate and rhodium nitrate. Then, the soaked productwas dried at 120° C. for 5 hours and calcinated at 400° C. for 4 hours.

Treatment examples 12 to 17

Each of the catalysts, 500 cc, obtained from preparation examples 6 to11 was filled in a reaction tube. Treatment of wastewater similar to thewastewater used in treatment example 11 was carried out under theconditions similar to treatment example 11.

Results obtained were shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                      kind of                                                                       metal     Amount of  treatment                                                soaked-in B component                                                                              efficiency                                 kind of       (B compo- in catalyst                                                                              of TOC                                     catalyst      nent)     (wt %)     (%)                                        ______________________________________                                        treatment                                                                             preparation                                                                             Ru        0.5      80                                       example 12                                                                            example 6                                                             treatment                                                                             preparation                                                                             Au        0.5      76                                       example 13                                                                            example 7                                                             treatment                                                                             preparation                                                                             Pd        0.5      81                                       example 14                                                                            example 8                                                             treatment                                                                             preparation                                                                             Ir        0.3      82                                       example 15                                                                            example 9                                                             treatment                                                                             preparation                                                                             Ag        3.0      77                                       example 16                                                                             example 10                                                           treatment                                                                             preparation                                                                             Rh        0.2      82                                       example 17                                                                             example 11                                                           ______________________________________                                    

Preparation examples 12 to 14

Similarly to preparation example 1, into 100 liter of water weredissolved ferric nitrate and other metal nitrates. To this solution,sodium hydroxide was added until pH 8.5 being indicated to form aprecipitate. Then, oxides of iron and added metals were obtained bycarrying out the procedure similar to preparation example

These oxides were molded by the procedure similar to preparationexample 1. Whereby, pellet type molded products (catalysts) of paticlediameter 5 mm φ and length 6 mm were obtained.

Treatment examples 18 to 20

Each of the catalysts, 500 cc, obtained from preparation examples 12 to14 was filled in a reaction tube. Treatment of wastewater similar to thewastewater used in treatment example 10 was carried out under theconditions similar to treatment example 10.

Results obtained were shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                                amount of  COD (Cr)                                                 kind of   oxide of   concen-                                                  metal     left-described                                                                           tration                                                  in added- metal      in treated                                 kind of       metal     in catalyst                                                                              water                                      catalyst      solution  (wt %)     (mg/l)                                     ______________________________________                                        treatment                                                                             preparation                                                                             Co        31.9     6,500                                    example 18                                                                            example 12                                                            treatment                                                                             preparation                                                                             Ni        23.8     8,200                                    example 19                                                                            example 13                                                            treatment                                                                             preparation                                                                             Ce        21.2     6,200                                    example 20                                                                            example 14                                                            ______________________________________                                    

Preparation example 15

Into 100 liter of water were dissolved 24.87 kg of ferrous sulfate[FeSO₄ ·7H₂ O] and 2.00 kg of cerous nitrate [Ce(NO₃)₃ ·6H₂ O]. Anobtained solution was well mixed. To this mixture maintained at about30° C. with well stirring, an aqueous ammonia was gradually addeddropwise until pH 9 being indicated, and an obtained mixture was stillstood for 24 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 16 hours. Then, it was calcinated at 600° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of Fe₂ O₃ and CeO₂, in which the Weight ratio betweenFe₂ O₃ and CeO₂ was 9 versus 1 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to aspherical shape of average paticle diameter 6 mm and calcinated at 500°C. for 4 hours under an air atmosphere.

Treatment example 21

The catalyst, 500 cc, obtained from preparation example 15 was filled ina reaction tube. Treatment of wastewater similar to the wastewater usedin treatment example 11 was carried out under the conditions similar totreatment example 11.

The above-mentioned treatment resulted in that treated wastewatercontaining 100 mg/l or less of thiophene, 10 mg/l or less of sodiumrhodanide and 200 mg/l or less of dimethyl sulfoxide was stablyobtained. In addition, TOC treatment efficiency was 69%.

Preparation example 16

The spherical molded product of the iron-cerium oxide obtained frompreparation example 15 was soaked in an aqueous ruthenium solution.Then, this soaked product was dried at 130° C. for 3 hours andcalcinated at 400° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.3 versus0.7 ratio by weight between the iron-cerium oxide and ruthenium,according to a fluorescence X-ray analysis.

Treatment example 22

The catalyst, 500 cc, obtained from preparation example 16 was filled ina reaction tube. Treatment of wastewater similar to the wastewater usedin treatment example 11 was carried out under the conditions similar totreatment example 11.

The above-mentioned treatment resulted in that treated wastewatercontaining 30 mg/l or less of thiophene, 10 mg/l or less of sodiumrhodanide and 10 mg/l or less of dimethyl sulfoxide was stably obtained.In addition, TOC treatment efficiency was 84%.

Comparative preparation examples 3 to 8

Similarly to preparation examples 6 to 11, the pellet-like moldedproduct of the oxide of titanium obtained from comparative preparationexample 1 was soaked in each of the aqueous metal salt solutions andcalcinated. Whereby, catalyst were obtained.

Comparative treatment examples 3 to 8

Each of the catalysts obtained from comparative preparation examples 3to 8 was filled in a reaction tube. Treatment of wastewater similar tothe wastewater used in treatment example 10 was carried out under theconditions similar to treatment example 10.

Results obtained were shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                                amount of  COD (Cr)                                                           left-described                                                                           concen-                                                    kind of metal      tration                                                    metal   component  in treated                                        kind of  soaked- in catalyst                                                                              water                                             catalyst in      (wt %)     (mg/l)                                     ______________________________________                                        comparative                                                                            comparative                                                                              Ru      0.5      14,000                                   treatment                                                                              preparation                                                          example 3                                                                              example 3                                                            comparative                                                                            comparative                                                                              Au      0.5      18,000                                   treatment                                                                              preparation                                                          example 4                                                                              example 4                                                            comparative                                                                            comparative                                                                              Pd      0.5      12,000                                   treatment                                                                              preparation                                                          example 5                                                                              example 5                                                            comparative                                                                            comparative                                                                              Ir      0.3      11,000                                   treatment                                                                              preparation                                                          example 6                                                                              example 6                                                            comparative                                                                            comparative                                                                              Ag      3.0      19,000                                   treatment                                                                              preparation                                                          example 7                                                                              example 7                                                            comparative                                                                            comparative                                                                              Rh      0.2      12,000                                   treatment                                                                              preparation                                                          example 8                                                                              example 8                                                            ______________________________________                                    

Comparative preparation examples 9 to 11

Similarly to preparation example 1, into 100 liter of water were added atitanyl sulfate solution and a metal nitrate. To this solution, sodiumhydroxide was added until pH 8.5 being indicated to form a precipitate.Then, an oxide of the titanium and added metal was obtained by carryingout the procedure similar to preparation example 1.

This oxide was molded by the procedure similar to preparation example 1.Whereby, a pellet-like molded product (catalysts) of paticle diameter 5mm φ and length 6 mm was obtained.

Comparative treatment examples 9 to 11

Each of the catalysts, 500 cc, obtained from comparative preparationexamples 9 to 11 was filled in a reaction tube. Treatment of wastewatersimilar to the wastewater used in treatment example 11 was carried outunder the conditions similar to treatment example 11.

Results obtained were shown in Table 7.

                  TABLE 7                                                         ______________________________________                                                                 amount of                                                            kind of  oxide of                                                             metal    left-described                                                                           treatment                                                 in added-                                                                              metal      efficiency                                       kind of  metal    in catalyst                                                                              of TOC                                           catalyst solution (wt %)     (%)                                       ______________________________________                                        comparative                                                                            comparative                                                                              Co       31.9     46                                      treatment                                                                              preparation                                                          example 9                                                                              example 9                                                            comparative                                                                            comparative                                                                              Ni       23.8     47                                      treatment                                                                              preparation                                                          example 10                                                                             example 10                                                           comparative                                                                            comparative                                                                              Ce       21.2     58                                      treatment                                                                              preparation                                                          example 11                                                                             example 11                                                           ______________________________________                                    

Preparation examples 17 to 19

Into 50 liter of water were dissolved 10 kg of ferric nitrate [Fe(NO₃)₃·9H₂ O]. To this solution maintained at about 30° C. with well stirring,an aqueous ammonia was gradually added dropwise until pH 8.5 beingindicated, and an obtained mixture was still stood for 16 hours to makea precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 16 hours. Then, it was calcinated at 600° C. for 8 hours under anair atmosphere. According to a X-ray diffraction analysis, an obtainedpowder consisted of Fe₂ O₃.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletshaving a particle diameter 5 mm φ and length 6 mm, and calcinated at500° C. for 4 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous solution of iridiumnitrate, platinum nitrate or ruthenium nitrate. These soaked productswere dried at 120° C. for 6 hours and then calcinated at 400° C. for 4hours.

Treatment examples 23 to 25

Using each of the catalysts obtained from the preparation examples 17 to19, treatment of wastewater containing 500 mg/l of trichloroethylene wascarried out by wet oxidation according to the following procedure.

Each of the catalysts (500 cc) was filled in a reaction tube and, from adown part of the reaction tube, preheated wastewater blended with airwas continuously introduced for 1,000 hours, the trichloroethyleneconcentration was measured at an entrance and exit of the reaction tubeto calculate the elimination percentage of trichloroethylene.

The reaction conditions were 250° C. at a reaction temperature, 70kg/cm² G at a reaction pressure, 0.5 liter per hour at the rate ofsupplying wastewater, and 10N liter per hour at the rate of supplyingair. Obtained results are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                                           elimination                                              kind of              percentage                                               metal     amount of  of                                                       soaked-in B component                                                                              trichloro-                                 kind of       (B compo- in catalyst                                                                              ethylene                                   catalyst      nent)     (wt %)     (%)                                        ______________________________________                                        treatment                                                                             preparation                                                                             Ir        0.3      94                                       example 23                                                                            example 17                                                            treatment                                                                             preparation                                                                             Pt        0.3      96                                       example 24                                                                            example 18                                                            treatment                                                                             preparation                                                                             Ru        1.0      92                                       example 25                                                                            example 19                                                            ______________________________________                                    

Preparation example 20

A compound consisting of titanium and iron was prepared by theundermentioned process and, as a titanium source, an aqueous sulfuricacid having the following composition was used.

TiOSO₄ . . . 250 g/l (as TiO₂)

total H₂ SO₄ . . . 1,100 g/l

Into 100 liter of water were dissolved 5.41 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O] and an obtained solution was well mixed With adding 5liter of an aqueous sulfuric acid solution of titanyl sulfate (titaniumoxysulfate) which has the above composition. To this mixture maintainedabout 30° C. with well stirring, an aqueous ammonia was gradually addeddropwise until pH 8 being indicated, and an obtained mixture was stillstood for 15 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂ and Fe₂ O₃, in which the weight ratio betweenTiO₂ and Fe₂ O₃ was 53.9 versus 46.1 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process,

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletsof paticle diameter 5 mm φ and length 6 mm and calcinated at 500° C. for3 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous palladium nitratesolution, dried at 120° C. for 6 hours, and calcinated at 400° C. for 3hours.

An obtained, completed catalyst showed composition having a 98 versus 2ratio by weight between a TiO₂ --Fe₂ O₃ compound and palladium,according to a fluorescence X-ray analysis.

Preparation example 21

Into 80 liter of water were dissolved 6.57 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O] and 2.17 kg of zirconium oxynitrate (zirconiumnitrate) [ZrO (NO₃)₂ ·2H₂ O ] with well mixing. To this mixturemaintained at about 30° C. with well stirring, an aqueous ammonia wasgradually added dropwise until pH 8 being indicated, and an obtainedmixture was still stood for 15 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, an obtainedpowder consisted of ZrO₂ and Fe₂ O₃, in which the weight ratio betweenZrO₂ and Fe₂ O₃ was 43.5 versus 56.5 according to a fluorescence X-rayanalysis.

Using this obtained powder a catalyst was prepared by the undermentionedprocess.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletshaving a particle diameter 5 mm φ and length 6 mm, and calcinated at500° C. for 3 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous ruthenium nitratesolution, dried at 120° C. for 6 hours and calcinated at 400° C. for 3hours.

An obtained, completed catalyst showed composition having a 95 versus 5ratio by weight between a ZrO₂ --Fe₂ O₃ compound and ruthenium,according to a fluorescence X-ray analysis.

Preparation example 22

Into 100 liter of water were dissolved 6.07 kg of ferric nitrate[Fe(NO₃)₃ ·9H₂ O] and an obtained solution was well mixed withdissolving 4 liter of an aqueous sulfuric acid solution of titanylsulfate (titanium oxysulfate) having the composition used in thepreparation example 20 and 1.34 kg of zirconium oxynitrate (zirconiumnitrate) [ZrO (NO₃)₃ ·2H₂ O]. To this mixture maintained at about 30° C.with well stirring, an aqueous ammonia was gradually added dropwiseuntil pH 8 being indicated, and an obtained mixture was still stood for15 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂, ZrO₂ and Fe₂ O₃, in which the weight ratiosamong TiO₂, ZrO₂ and Fe₂ O₃ were 35.5, 21.9 and 42.6, respectively,according to a fluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletshaving a particle diameter 5 mmφ and length 6 mm and calcinated at 500°C. for 3 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous platinum nitratesolution, dried at 120° C. for 6 hours, and calcinated at 400° C. for 3hours.

An obtained, completed catalyst showed composition having a 99 versus 1ratio by weight between a TiO₂ --ZrO₂ --Fe₂ O₃ compound and platinum,according to a fluorescence X-ray analysis.

Preparation examples 23 and 24

The procedure of preparation example 20 was repeated except that theratio between TiO₂ and Fe₂ O₃ was varied as follows.

    ______________________________________                                        TiO.sub.2 versus Fe.sub.2 O.sub.3 (weight ratio)                              ______________________________________                                        Preparation example 23                                                                          80 versus 20                                                Preparation example 24                                                                          15 versus 85                                                ______________________________________                                    

Preparation examples 25 to 27

Pellets of the TiO₂ --ZrO₂ --Fe₂ O₃ compound obtained from thepreparation example 22 were soaked in each of an aqueous chloroauricacid solution, aqueous rhodium nitrate solution and aqueous iridiumnitrate solution, dried at 120° C. for 6 hours, and calcinated at 400°C. for 3 hours.

Obtained, completed catalysts had the below-described composition byweight ratios, according to a fluorescence X-ray analysis.

    ______________________________________                                        Preparation example 25                                                                        (TiO.sub.2 --ZrO.sub.2 --Fe.sub.2 O.sub.3 compound)                           versus Au = 90 versus 10                                      Preparation example 26                                                                        (TiO.sub.2 --ZrO.sub.2 --Fe.sub.2 O.sub.3 compound)                           versus Rh = 99 versus 1                                       Preparation example 27                                                                        (TiO.sub.2 --ZrO.sub.2 --Fe.sub.2 O.sub.3 compound)                           versus Ir = 95 versus 5                                       ______________________________________                                    

Treatment examples 26 to 33

Using each of the catalysts obtained from the preparation examples 20 to27, wastewater treatment was carried out by wet oxidation according tothe following procedure.

Each of the catalysts (1000 cc) was filled in a reaction tube made of astainless steel and, from a down part of the reaction tube, preheatedwastewater blended with air containing oxygen in a concentration ofabout 21% was continuously introduced for 5,000 hours, the COD (Cr)concentration and total nitrogen amount were measured at an entrance andexit of the reaction tube to calculate their elimination percentages.Meanwhile, before treatment, wastewater contained 15,000 mg/l ofdimethylformamide and showed 20,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 230N liter per hour at the rate of supplyingair. The obtained results are shown in Table 9.

                  TABLE 9                                                         ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 99.9       99.5                                         example 26                                                                              example 20                                                          treatment preparation 99.9       99.1                                         example 27                                                                              example 21                                                          treatment preparation 99.9       99.0                                         example 28                                                                              example 22                                                          treatment preparation 99.9       99.4                                         example 29                                                                              example 23                                                          treatment preparation 99.9       99.6                                         example 30                                                                              example 24                                                          treatment preparation 99.6       99.0                                         example 31                                                                              example 25                                                          treatment preparation 99.7       98.5                                         example 32                                                                              example 26                                                          treatment preparation 99.5       98.3                                         example 33                                                                              example 27                                                          ______________________________________                                    

As seen in Table 9, in a continuous operation for 5,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Treatment examples 34 to 38

According to the treatment example 26, wastewater treatment was carriedout by wet oxidation using each of the catalysts obtained from thepreparation examples 20 to 24. Wastewater to be treated contained 20,000mg/l of glycine and showed 19,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 160N liter per hour at the rate of supplyingair. The obtained results are shown in Table 10.

                  TABLE 10                                                        ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 99.8       99.5                                         example 34                                                                              example 20                                                          treatment preparation 99.9       99.1                                         example 35                                                                              example 21                                                          treatment preparation 99.9       99.0                                         example 36                                                                              example 22                                                          treatment preparation 99.9       99.3                                         example 37                                                                              example 23                                                          treatment preparation 99.9       99.4                                         example 38                                                                              example 24                                                          ______________________________________                                    

As seen in Table 10, in a continuous operation for 3,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Treatment examples 39 to 43

According to the treatment example 26, wastewater treatment was carriedout by wet oxidation using each of the catalysts obtained from thepreparation examples 20 to 24. Wastewater to be treated contained 10,000mg/l of ethanolamine and showed 12,000 mg/l in the COD (Cr)concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 140N liter per hour at the rate of supplyingair. Obtained results are shown in Table 11.

                  TABLE 11                                                        ______________________________________                                                                     elimination                                                                   percentage                                                         elimination                                                                              of total                                                           percentage nitrogen                                                 kind of   of COD (Cr)                                                                              amount                                                   catalyst  (%)        (%)                                              ______________________________________                                        treatment preparation 99.0       99.0                                         example 39                                                                              example 20                                                          treatment preparation 98.8       98.8                                         example 40                                                                              example 21                                                          treatment preparation 98.8       98.9                                         example 41                                                                              example 22                                                          treatment preparation 99.0       98.6                                         example 42                                                                              example 23                                                          treatment prreparation                                                                              99.0       98.8                                         example 43                                                                              example 24                                                          ______________________________________                                    

As seen in Table 11, in a continuous operation for 3,000 hours under theforementioned conditions, decrease in the elimination percentages of theCOD (Cr) and total nitrogen amount was not recognized.

Comparative preparation example 12

The procedure of preparation example 20 was repeated to obtain acatalyst except that an aqueous solution of ferric nitrate was not used.Composition of an obtained, completed catalyst showed a weight ratio of98 versus 2 between TiO₂ and palladium.

Comparative preparation example 13

Into 4 liter of an aqueous sulfuric acid solution of titanyl sulfate(titanium oxysulfate) having the composition used in the preparationexample 20 was added with mixing 1.44 kg of zirconium oxynitrate[ZrO(NO₃)₂ ·2H₂ O]. To this mixture maintained at about 30° C. with wellstirring, an aqueous ammonia was gradually added dropwise until pH 8being indicated, and an obtained mixture was still stood for 15 hours tomake a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 10 hours. Then, it was calcinated at 700° C. for 5 hours under anair atmosphere. Composition of an obtained powder showed a weight ratioof 60.2 versus 39.8 between TiO₂ and ZrO₂.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletshaving a particle diameter 5 mmφ and length 6 mm and calcinated at 500°C. for 3 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous iron nitratesolution, dried at 120° C. for 6 hours, and calcinated at 400° C. for 3hours.

An obtained, completed catalyst showed composition having a 85 versus 15ratio by weight between a TiO₂ --ZrO₂ compound and Fe₂ O₃.

Comparative treatment examples 12 and 13

Wastewater treatment by wet oxidation was carried out by the procedureof treatment example 26 except that each of the catalysts obtained fromthe comparative preparation examples 12 and 13 was used.

Results obtained are shown in Table 12.

                                      TABLE 12                                    __________________________________________________________________________                  initial     after 500 hours                                                         elimination elimination                                                 elimination                                                                         percentage                                                                          elimination                                                                         percentage                                                  percentage                                                                          of total                                                                            percentage                                                                          of total                                                    of    nitrogen                                                                            of    nitrogen                                             kind of                                                                              COD (Cr)                                                                            amount                                                                              COD (Cr)                                                                            amount                                               catalyst                                                                             (%)   (%)   (%)   (%)                                           __________________________________________________________________________    comparative                                                                          comparative                                                                          72.0  75.0  42.0  36.0                                          treatment                                                                            preparation                                                            example 12                                                                           example 12                                                             comparative                                                                          comparative                                                                          50.5  47.5  37.0  25.5                                          treatment                                                                            preparation                                                            example 13                                                                           example 13                                                             __________________________________________________________________________

As seen in Table 12, in the comparative treatment example 12 where acatalyst not containing the component was used as well as in thecomparative treatment example 13 where a catalyst containing iron as a Bcomponent, the COD (Cr)-elimination and total nitrogen-eliminationpercentages are both lower than the cases where the catalysts of thisinvention were used, and furthermore, a large decrease in theCOD(Cr)-elimination and total nitrogen-elimination percentages wasobserved in a continuous operation of 500 hours.

Preparation example 28

Into 100 liter of water were added 9 liter of an aqueous titanyl sulfatesolution (which has the same composition as the solution used inpreparation example 20) and 4 liter of an aqueous ferrous sulfate [FeSO₄; 500 g/l solution, and these solutions were well mixed each other. Tothis mixture maintained at about 30° C. with well stirring, an aqueousammonia was gradually added dropwise until pH 7 being indicated, and anobtained mixture was still stood for 20 hours to make a precipitate(gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 12 hours. Then, it was calcinated at 700° C. for 6 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂ and Fe₂ O₃, in which the weight ratio betweenTiO₂ and Fe₂ O₃ was 75.0 versus 25.0 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to aspherical shape of average paticle diameter 5 mm and calcinated at 500°C. for 3 hours under an air atmosphere.

The thus-obtained, spherical molded product was soaked in an aqueousruthenium nitrate solution, dried at 120° C. for 6 hours, and calcinatedat 400° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.7 versus0.3 ratio by weight between a TiO₂ --Fe₂ O₃ compound and Ru, accordingto a fluorescence X-ray analysis.

Treatment example 44

Using the catalyst obtained from preparation example 28, wastewaterhaving the below-mentioned composition was treated.

    ______________________________________                                        pH                  13                                                        Na.sub.2 S          8%                                                        NaSH                3%                                                        NaCO.sub.3          3%                                                        TOD                 100,000 mg/l                                              ______________________________________                                    

The catalyst (500 cc) was filled in a reaction tube made of a stainlesssteel of a wet oxidation column and, from a down part of the reactiontube, preheated wastewater blended with air was continuously introducedfor 1,000 hours, the concentrations of sulfide ion (S²⁻), thiosulfateion and COD (Cr) were measured at an entrance and exit of the reactiontube.

The reaction conditions were 150° C. at a reaction temperature, 9 kg/cm²G at a reaction pressure, 0.5 liter per hour at the rate of supplyingwastewater, and 200N liter per hour at the rate of supplying air [ratioof O₂ /TOD (amount of oxygen in air/total amount of consumed oxygen) is1.2].

As a result, treated water was stably obtained, which contained COD(Cr), sulfide ion and thiosulfate ion in concentrations of 3000 mg/l orless, 0.1 mg/l or less and 4500 mg/l or less, respectively.

Comparative treatment example 14

The procedure of treatment example 44 was repeated except that anycatalyst was not filled in a wet oxidation column and the column wasempty.

As a result, treated water contained COD (Cr), sulfide ion andthiosulfate ion in concentrations of 23,000 mg/l, 20 mg/l and 30,000mg/l, respectively.

Treatment example 45

Wastewater having the below-mentioned composition was treated by theprocedure similar to treatment example 44, except that the catalyst in awet oxidation column was changed.

    ______________________________________                                               pH           13                                                               Na.sub.2 S.sub.2 O.sub.3                                                                   1.7%                                                             NaOH         1.0%                                                             TOD          8,600 mg/l                                                ______________________________________                                    

A catalyst used in the present treatment example was the catalystobtained from preparation example 28. This catalyst (500 cc) was filledin a wet oxidation column.

The above-mentioned treatment resulted in that treated water containing70 mg/l or less of COD (Cr), 100 mg/l or less of thiosulfate ion wasstably obtained.

Comparative treatment example 15

The procedure of treatment example 45 was repeated except that anycatalyst was not filled in a wet oxidation column and the column wasempty.

As a result, 4300 mg/l of COD (Cr) and 6,000 mg/l of thiosulfate ionremained in treated water.

Treatment example 46

Wastewater having the below-mentioned composition was treated by theprocedure similar to treatment example 44, except that the catalyst in awet oxidation column was changed.

    ______________________________________                                        pH                  13                                                        Na.sub.2 S          2.4%                                                      Na.sub.2 S.sub.2 O.sub.3                                                                          0.9%                                                      Na.sub.2 SO.sub.2   0.2%                                                      NaOH                0.5%                                                      TOD                 25,000 mg/l                                               ______________________________________                                    

A catalyst used in the present treatment example was the catalystobtained from preparation example 28. This catalyst (500 cc) was filledin a wet oxidation column.

The above-mentioned treatment resulted in that treated water containing230 mg/l or less of COD (Cr), 350 mg/l or less of thiosulfate ion wasstably obtained. In addition, both sulfide ion and sulfite ion were 0.01mg/l or less.

Comparative treatment example 16

The procedure of treatment example 46 was repeated except that anycatalyst was not filled in a wet oxidation column and the column wasempty.

As a result, 7,200 mg/l of COD (Cr), 5 mg/l of sulfide ion and 10,000mg/l of thiosulfate ion remained in treated water. In addition, sulfiteion was 0.01 mg/l or less.

Preparation example 29

Into 100 liter of water were added 7 liter of an aqueous titanyl sulfatesolution (which has the same composition as the solution used inpreparation example 20) and 3.80 kg of ferric nitrate [Fe(NO₃)₃ ·9H₂ O],and these were well mixed. To this mixture maintained at about 30° C.with well stirring, an aqueous ammonia was gradually added dropwiseuntil pH 7 being indicated, and an obtained mixture was still stood for16 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 20 hours. Then, it was calcinated at 700° C. for 6 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂ and Fe₂ O₃, in which the weight ratio betweenTiO₂ and Fe₂ O₃ was 70.0 versus 30.0 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to aspherical shape of average paticle diameter 6 mm and calcinated at 500°C. for 4 hours under an air atmosphere.

The thus-obtained, spherical molded product was soaked in an aqueouschloroplatinic acid solution, dried at 120° C. for 6 hours, andcalcinated at 400° C. for 6 hours.

An obtained, completed catalyst showed composition having a 99.6 versus0.4 ratio by weight between a TiO₂ --Fe₂ O₃ compound and Pt, accordingto a fluorescence X-ray analysis.

Treatment example 47

Using the catalyst obtained from preparation example 29 and according tothe below-mentioned procedure, wastewater was treated by a wetoxidation. The catalyst (3,000 cc) was filled in a reaction tube made ofa stainless steel and from a down part of the reaction tube, preheatedwastewater blended with air was continuously introduced for 500 hours, aCOD (Cr) concentration, an amount of thiophene and an amount of sodiumdodecyl sulfate were measured at an entrance and exit of the reactiontube to calculate treatment efficiency.

Here, conditions of wastewater provided for treatment were 3.5 g/l in anamount of thiophene, 20 g/l in an amount of sodium dodecyl sulfate, 16.2g/l in other oil content, 21.7 g/l in TOC, and before treatment, causticsoda had been added to the wastewater until pH 13 being indicated. Thereaction conditions were 240° C. at a reaction temperature, 70 kg/cm² Gat a reaction pressure, 0.9 per hour at space velocity of wastewater(empty column standard), 6 m per hour at linear velocity of wastewater.Air was introduced to the reaction tube in such an amount that the ratioof O₂ /TOD (amount of oxygen in air/total amount of consumed oxygen) is1.0.

As a result, elimination percentages of thiophene, sodium dodecylsulfate, and TOC were 97.0%, 89.5%, and 82.0%, respectively. Inaddition, pH of treated water was 8.

Comparative treatment example 17

The procedure of treatment example 47 was repeated except that anycatalyst was not filled in a wet oxidation column and the column wasempty.

As a result, elimination percentages of thiophene, sodium dodecylsulfate, and TOC were 42.0%, 37.0%, and 34.5%, respectively. Inaddition, pH of treated water was 11.

Preparation example 30

Into 100 liter of water were added 5 liter of an aqueous titanyl sulfatesolution (which has the same composition as the solution used inpreparation example 20). 10.66 kg of ferric nitrate [Fe(NO₃)₃ ·9H₂ O]and 1.32 kg of cerous nitrate [Ce(NO₃)₃ ·6H₂ O], and these were wellmixed. To this mixture maintained at about 30° C. with well stirring, anaqueous ammonia was gradually added dropwise until pH 8 being indicated,and an obtained mixture was still stood for 24 hours to make aprecipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 16 hours. Then, it was calcinated at 700° C. for 6 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂, Fe₂ O₃ and CeO₂, in which the weight ratioamong TiO₂, Fe₂ O₃ and CeO₂ was 31.2:52.6:16.2 according to afluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to aspherical shape of average paticle diameter 5 mm and calcinated at 500°C. for 4 hours under an air atmosphere.

The thus-obtained, spherical molded product was soaked in an aqueousruthenium nitrate solution, dried at 120° C. for 6 hours, and calcinatedat 450° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.4 versus0.6 ratio by weight between a TiO₂ --Fe₂ O₃ --CeO₂ compound and Ru,according to a fluorescence X-ray analysis.

Treatment example 48

Using the catalyst obtained from preparation example 30, wastewatercontaining 100 mg/l of ethyl bromide was treated by the below-mentionedprocess.

The catalyst (500 cc) was filled in a reaction tube made of titanium ofa wet oxidation column and, from a down part of the reaction tube,preheated wastewater blended with air was continuously introduced for1,000 hours, the concentrations of ethyl bromide and bromide ion weremeasured at an entrance and exit of the reaction tube.

The reaction conditions were 270° C. at a reaction temperature, 80kg/cm² G at a reaction pressure, 0.5 liter per hour at the rate ofsupplying wastewater, and 10N liter per hour at the rate of supplyingair.

As a result, the elimination percentage of ethyl bromide was 99%, andany organic bromine compound except ethyl bromide was not detected intreated water by GC-ECD method. In addition, the bromide ionconcentration in the treated water was 73 mg/l and ethyl bromide was notdetected at all in waste gas.

Preparation example 31

Into 100 liter of water were added 5 liter of an aqueous titanyl sulfatesolution (which has the same composition as the solution used inpreparation example 20) and 7.56 kg of ferric nitrate [Fe(NO₃)₃ ·9H₂ O],and these were well mixed. To this mixture maintained at about 30° C.with well stirring, an aqueous ammonia was gradually added dropwiseuntil pH 7 being indicated, and an obtained mixture was still stood for16 hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, and dried at 120°C. for 20 hours. Then, it was calcinated at 700° C. for 6 hours under anair atmosphere. According to a X-ray diffraction analysis, the obtainedpowder consisted of TiO₂ and Fe₂ O₃, in which the weight ratio betweenTiO₂ and Fe₂ O₃ was 45.5 versus 54.5 according to a fluorescence X-rayanalysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device tohoneycomb structure having a penetrating hole-corresponding diameter of10 mm, a cell wall thickness of 1 mm and an opening ratio of 83%, andthen calcinated at 500° C. for 4 hours under an air atmosphere.

The thus-obtained, honeycomb type molded product was soaked in anaqueous palladium nitrate solution, dried at 120° C. for 6 hours, andcalcinated at 400° C. for 4 hours.

An obtained, completed catalyst showed composition having a 99.3 versus0.7 ratio by weight between a TiO₂ --Fe₂ O₃ compound and Pd, accordingto a fluorescence X-ray analysis.

Treatment example 49

According to treatment example 48, the catalyst obtained frompreparation example 31 was filled in a wet oxidation column, andwastewater containing 50 mg/l of dichlorobenzene was treated. However,in the present treatment example, a temperature at an entrance of areaction vessel was 230° C. , a reaction pressure was 60 kg/cm² G, andan air amount was 5 liter per hour. Other conditions were similar totreatment example 48.

As a result, the elimination percentage of dichlorobenzene was 89%, andany organic chlorine compound except dichlorobenzene was not detected intreated water. In addition, the chloride ion concentration in thetreated water was 21 mg/l and dichlorobenzene was not detected at all inwaste gas.

Treatment example 50

The procedure of treatment example 49 was repeated except that a gascontaining oxygen in concentration of 70% was used.

As a result, the elimination percentage of dichlorobenzene was 94%, andany organic chlorine compound except dichlorobenzene was not detected intreated water. In addition, the chloride ion concentration in thetreated water was 54 mg/l and dichlorobenzene was not detected at all inwaste gas.

Preparation example 32

The honeycomb type molded product of a titanium-iron n oxide obtainedfrom preparation example 31 was soaked in an aqueous rhodium nitratesolution, dried at 120° C. for 6 hours, and calcinated at at 400° C. for3 hours to obtain a catalyst.

Treatment example 51

The catalyst obtained from preparation example 32 was filled in a wetoxidation column, and wastewater treatment was carried out. In addition,wastewater containing 500 mg/l of trichloroethylene was used as modelwastewater. The model wastewater did not contain chloride ion. Thereaction was carried out under the conditions of 250° C. and 70 kg/cm²G. Other conditions and flow were similar to treatment example 48. As aresult, the elimination percentage of trichloroethylene was 95%.

Comparative treatment example 18

According to treatment Example 51, wastewater similar to the wastewaterused in treatment example 51 was treated under the conditions similar totreatment example 51. However, any catalyst was not filled in a wetoxidation column and the column was empty. As a result, the eliminationpercentage of trichloroethylene was 32%.

Preparation example 33

Into 100 liter of water, were added 4 liter of an aqueous titanylsulfate solution (which has the same composition in the solution used inpreparation example 20), and these were well mixed each other. To thismixture maintained at about 30° C. with well stirring, an aqueousammonia was gradually added dropwise until pH 8 being indicated, and anobtained mixture was still stood for 15 hours to make a precipitate(gel).

This gel was taken by filtration and washed with water.

To the gel, 1.67 kg of a hydroxide of iron (α-FeOOH) were added andthese were mixed and well kneaded by a kneader and dried at 120° C. for10 hours. Then, the resulting kneaded mixture was calcinated at 700° C.for 5 hours under an air atmosphere to obtain a powder. According to aX-ray diffraction analysis, the obtained powder consisted of TiO₂ andFe₂ O₃ in which the weight ratio between TiO₂ and Fe₂ O₃ was 40 versus60 according to a fluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

Water, the obtained powder and starch were mixed and well kneaded by akneader. This kneaded product was molded by a molding device to pelletsof particle diameter 5 mm φ and length 6 mm and calcinated at 500° C.for 3 hours under an air atmosphere.

The pellets thus-obtained were soaked in an aqueous ruthenium nitratesolution, dried at 120° C. for 6 hours, and calcinated at 400° C. for 3hours.

An obtained, completed catalyst showed composition having a 98 versus 2ratio by weight between a TiO₂ --Fe₂ O₃ compound and ruthenium,according to a fluorescence X-ray analysis.

Treatment example 52

Using the catalyst obtained from the preparation example 33, wastewatertreatment was carried out by wet oxidation according to the followingprocedure.

The catalyst (1000 cc) was filled in a reaction tube made of a stainlesssteel and, from a down part of the reaction tube, preheated wastewaterblended with air containing oxygen in concentration of about 21% wascontinuously introduced for 5,000 hours, the COD (Cr) concentration andtotal nitrogen amount were measured at an entrance and exit of thereaction tube to calculate their elimination percentages. Meanwhile,before treatment, wastewater contained 15,000 mg/l of dimethylformamideand showed 20,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 230N liter per hour at the rate of supplyingair. The obtained results are shown in Table 13.

According to the treatment example 26, wastewater treatment was carriedout by wet oxidation using the catalyst obtained from the preparationexample 33. Wastewater to be treated contained 20,000 mg/l of glycineand showed 19,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 160N liter per hour at the rate of supplyingair. The obtained results are shown in Table 13.

Treatment example 54

According to the treatment example 26, wastewater treatment was carriedout by wet oxidation using the catalyst obtained from the preparationexample 33. Wastewater to be treated contained 10,000 mg/l ofethanolamine and showed 12,000 mg/l in the COD (Cr) concentration.

The reaction conditions were 200° C. at a reaction temperature, 40kg/cm² G at a reaction pressure, 2 liter per hour at the rate ofsupplying wastewater, and 140N liter per hour at the rate of supplyingair. Obtained results are shown in Table 13.

                  TABLE 13                                                        ______________________________________                                                                     Elimination                                                       Elimination percentage                                                        percentage  of total                                                 Kind of  of COD (Cr) nitrogen                                                 catalyst %           amount (%)                                       ______________________________________                                        Treatment Preparation                                                                              99.0        98.7                                         example 52                                                                              example 33                                                          Treatment Preparation                                                                              98.5        98.5                                         example 53                                                                              example 33                                                          Treatment Preparation                                                                              98.0        98.5                                         example 54                                                                              example 33                                                          ______________________________________                                    

Preparation example 34

Into 30 liter of water was added 2.4 liter of the same aqueous sulfuricacid solution of titanyl sulfate (titanium oxysulfate) as that for thepreparation example 20 with well mixing. To the resulting mixturemaintained at about 30° C. with well stirring, aqueous ammonia wasgradually added dropwise until pH 8 being indicated, and the resultingmixture was still stood for 15 hours to make a precipitate (gel).

This gel was taken by filtration and washed with water. To the resultinggel was added 2.67 kg of a hydroxide of iron (α-FeOOH), and they weremixed and well kneaded by a kneader, dried at 120° C. for 10 hours, andcalcined at 700° C. for 5 hours under an air atmosphere to obtain apowder. According to a X-ray diffraction analysis, the obtained powderconsisted of TiO₂ and Fe₂ O₃ in which the weight ratio of TiO₂ : Fe₂ O₃was 20:80 according to fluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

To the powder were added 0.6 liter of an aqueous ruthenium nitratesolution (Ru content: 50 g/l), 0.15 liter of an aqueous palladiumnitrate solution (Pd content: 100 g/l), water and starch, and they weremixed and well kneaded by a kneader. The resulting kneaded product wasmolded by a molding device to pellets of particle diameter 5 mmφ andlength 6 mm and calcined at 400° C. for 3 hours under an air atmosphere.

The resulting completed catalyst showed composition in which the weightratio of TiO₂ : Fe₂ O₃ : Ru: Pd was 19.7:78.8:1:0.5 according to afluorescence X-ray analysis.

Preparation example 35

Into 100 liter of water were added 5 liter of the same aqueous sulfuricacid solution of titanyl sulfate (titanium oxysulfate) as that for thepreparation example 20 and 5.41 kg of ferric nitrate [Fe(NO₃)₃ --9H₂ O)]with well mixing. To the resulting mixture maintained at about 30° C.with well stirring, aqueous ammonia was gradually added dropwise untilpH 8 being indicated, and the resulting mixture was still stood for 15hours to make a precipitate (gel).

This gel was taken by filtration, washed with water, dried at 120° C.for 10 hours, and calcined at 700° C. for 5 hours under an airatmosphere to obtain a powder. According to a X-ray diffractionanalysis, the obtained powder consisted of TiO₂ and Fe₂ O₃ ; in whichthe weight ratio of TiO₂ : Fe₂ O₃ was 53.9:46.1 according to afluorescence X-ray analysis.

Using this obtained powder, a catalyst was prepared by theundermentioned process.

To the powder were added 0.46 liter of an aqueous palladium nitratesolution (Pd content: 100 g/l), water and starch, and they were mixedand well kneaded by a kneader. The resulting kneaded product was moldedby a molding device to pellets of particle diameter 5 mm φ and length 6mm and calcined at 400° C. for 3 hours under an air atmosphere.

The resulting completed catalyst showed composition in which the weightratio of TiO₂ : Fe₂ O₃ : Pd was 52.9:45.2:1.9 according to fluorescenceX-ray analysis.

Treatment example 55

The procedure of the treatment example 52 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 34 was used instead of the catalystobtained from the preparation example 33. Obtained results are shown inTable 14.

Treatment example 56

The procedure of the treatment example 53 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 34 was used instead of the catalystobtained from the preparation example 33. Obtained results are shown inTable 14.

Treatment example 57

The procedure of the treatment example 54 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 34 was used instead of the catalystobtained from the preparation example 33. Obtained results are shown inTable 14.

Treatment example 58

The procedure of the treatment example 52 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 35 was used instead of the catalystobtained from the preparation example 33. Obtained results are shown inTable 14.

Treatment example 59

The procedure of the treatment example 53 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 35 was used instead of the catalystobtained from the preparation example 33. Obtained results are in Table14.

Treatment example 60

The procedure of the treatment example 54 was repeated to carry outwastewater treatment by wet oxidation except that the catalyst obtainedfrom the preparation example 35 was used instead of the catalystobtained form the preparation example 33. Obtained results are shown inTable 14.

                  TABLE 14                                                        ______________________________________                                                                     Elimination                                                       Elimination percentage                                                        percentage  of total                                                 Kind of  of COD (Cr) nitrogen                                                 catalyst %           amount (%)                                       ______________________________________                                        Treatment Preparation                                                                              99.5        99.0                                         example 55                                                                              example 34                                                          Treatment Preparation                                                                              99.2        99.0                                         example 56                                                                              example 34                                                          Treatment Preparation                                                                              98.8        98.5                                         example 57                                                                              example 34                                                          Treatment Preparation                                                                              98.0        97.5                                         example 58                                                                              example 35                                                          Treatment Preparation                                                                              97.6        97.2                                         example 59                                                                              example 35                                                          Treatment Preparation                                                                              97.5        96.4                                         example 60                                                                              example 35                                                          ______________________________________                                    

It is claimed:
 1. A catalyst for treating wastewater, said catalystconsisting of an A component, which is at least one material selectedfrom the group consisting of an oxide powder and a calcined, moldedproduct of said oxide powder, and a B component, which has oxidationactivity and is added on said A component, wherein;particles of saidoxide powder consisting of an oxide of iron and an oxide of at least oneelement selected from the group consisting of titanium, silicon andzirconium, and said B component consisting of a metal or compound of atleast one element selected from the group consisting of cobalt, nickel,cerium, silver, gold, platinum, palladium, rhodium, ruthenium andiridium; and wherein the A component is contained in a range of from 90to 99.95% by weight and the B component is contained in a range of from0.05 to 10 % by weight, wherein a total of the A and B components is 100% by weight, and in the A component, iron is in a range of from 4.95% to95% by weight as an oxide and at least one kind of element selected froma group consisting of titanium, silicon and zirconium is in a range offrom 4.95 to 95% by weight as an oxide,